Process for the preparation of 2,4,6-trifluoro-1,3,5-triazine

ABSTRACT

A process for the preparation of 2,4,6-trifluoro-1,3,5-triazine (cyanuric fluoride) in high purity and high yield at relatively low temperatures by reacting 2,4,6-trichloro-1,3,5-triazine (cyanuric fluoride [sic]) or mixed chlorinated/fluorinated 1,3,5-triazines with at least the equivalent amount of sodium fluoride, potassium fluoride or cesium fluoride or any desired mixture of these alkali metal fluorides in a dipolar aprotic solvent at temperatures from about 30° C. to about 110° C. and isolating the 2,4,6-trifluoro-1,3,5-triazine formed by distillation.

FIELD OF THE INVENTION

The invention relates to an improved process for the preparation of2,4,6-trifluoro-1,3,5-triazine (cyanuric fluoride) in high purity andhigh yield by reaction of cyanuric chloride with an alkali metalfluoride in a dipolar aprotic solvent at relatively low temperatures.Cyanuric fluoride is a useful starting compound for agrochemicals,pharmaceuticals, dyes, photochemicals and optical brighteners.

PRIOR ART

It is known that cyanuric fluoride can be prepared by fluorination ofcyanuric chloride with sodium fluoride in a dipolar aprotic solvent(Tullock, Coffman, J. org. Chem. 25, 2016 (1960)). In this process,cyanuric chloride is added to a suspension of sodium fluoride insulfolane and the reaction mixture is heated from 45° C. to 248° C. Thecyanuric fluoride formed is distilled off from the reaction mixture. Theyield is 74% of theory. According to DE-OS 3,727,973, cyanuric fluorideis obtained by the same method. 75° C. is already mentioned here as thelowest temperature for the reaction. According to Example A and lines 11to 15, column 2 (description), the reaction mixture must finally beheated to 220° C. in order to obtain cyanuric fluoride approximatelyquantitatively, i.e. in 87% yield. By-products mentioned are, interalia, partially fluorinated substances, such as6-chloro-2,4-difluorotriazine, which superficially indicates anincomplete reaction.

A slightly altered process is described in EP-0,035,704. Cyanuricchloride or mixed chlorinated/fluorinated 1,3,5-triazines, if desired inthe form of a melt or dissolved in a dipolar aprotic solvent, aremetered into a suspension of sodium fluoride in a dipolar aproticsolvent, in particular sulfolane, which is heated to 120° C. to 220° C.,in particular 140° to 160° C. Cyanuric fluoride is obtained from thereaction mixture by distillation, the distillation even having to becarried out in vacuo in the presence of a component of intermediateboiling point in order to be able to remove the cyanuric fluoride formedcompletely.

In these known processes, the reaction mixture is kept above about 120°C. over a relatively large part of the reaction time (Tullock, Coffman)or at temperatures above 120° C., preferably at 140° C.-160° C., overthe entire reaction time (EP-0,035,704). Even with the addition of phasetransfer catalysts, such as, for example, 18-crown-6 (CS) 247,969, JP61,047,465), temperatures of about 140°-400° C. are necessary in orderto obtain cyanuric fluoride from cyanuric chloride using alkali metalfluorides in a dipolar aprotic solvent.

These processes thus confirm the prejudice prevailing up to now that thepreparation of cyanuric fluoride (2,4,6-trifluoro-1,3,5-triazine) fromcyanuric chloride and potassium fluoride requires very high reactiontemperatures (HOUBEN-WEYL, volume V/3, 1962).

AIM OF THE INVENTION

An improved process for the preparation of2,4,6-trifluoro-1,3,5-triazine (cyanuric fluoride) in high purity andhigh yield at relatively low temperatures.

ESSENCE OF THE INVENTION

According to the invention, it has surprisingly been found that2,4,6-trifluoro-1,3,5-triazine (cyanuric fluoride) can advantageously beprepared in high purity and virtually quantitative yield at relativelylow temperatures by reacting 2,4,6-trichloro-1,3,5-triazine (cyanuricchloride) or mixed chlorinated/fluorinated 1,3,5-triazines with at leastthe equivalent amount of sodium fluoride, potassium fluoride or cesiumfluoride or any suitable mixture of these alkali metal fluorides in adipolar aprotic solvent at a temperature from about 30° C. to about 110°C., preferably about 50° C. to about 105° C., in particular about 70° C.to about 100° C.

In particular, a process can be used in which cyanuric chloride and/ormixed chlorinated/fluorinated 1,3,5-triazines, the alkali metal fluorideor mixtures of the alkali metal fluorides and the dipolar aproticsolvent are mixed and allowed to heat to the desired reactiontemperature (utilization of the heat of reaction liberated in thereaction) or are heated to the desired reaction temperature.

However, a process can also be used in which the cyanuric chloride ismetered into the suspension of the alkali metal fluoride or the mixtureof the alkali metal fluorides in a dipolar aprotic solvent as a solid,as a melt or dissolved or suspended in an inert solvent.

A further embodiment of the process according to the invention consistsin metering the alkali metal fluoride or the mixture of the alkali metalchlorides into the mixture of cyanuric chloride and/or mixedchlorinated/fluorinated 1,3,5-triazines and the dipolar aprotic solventas a solid or as a suspension in an inert solvent.

Finally, a process can also be used in which the cyanuric chloride,mixed with or dissolved in mixed chlorinated/fluorinated1,3,5-triazines, is metered into the suspension of the alkali metalfluoride or the mixture of alkali metal fluorides in a dipolar aproticsolvent, if desired with the addition of an inert solvent.

A suitable dipolar aprotic solvent for the process according to theinvention is any dipolar aprotic solvent which it is known can beemployed in chlorine/fluorine exchange reactions and is inert to thehalogenated triazines. Sulfolane is particularly suitable.

It is expedient to employ the alkali metal fluoride in a molar excess ofabout 5 to about 50%, preferably about 10 to about 20%, compared to therequired equivalent amount, relative to the cyanuric chloride. Indeed, amolar excess of over 50% can be used, but there is virtually no longerany advantage associated with this and the cost-efficiency of theprocess suffers.

The process can be carried out both at normal pressure and at reducedpressure or elevated pressure.

Inasmuch as "inert solvents" are mentioned in the embodiments of theprocess mentioned above, in this case these are any suitable solventswhich are inert under the reaction conditions to the starting and finalcompounds of the process, such as, for example, chlorobenzene,dichlorobenzene, toluene, xylene or tetrachloroethylene, or the dipolaraprotic solvent employed as the reaction medium or another dipolaraprotic solvent which is also inert under the reaction conditions to thestarting and final compounds.

The particular advantage of the process according to the invention is,above all, that hitherto the reaction had to be carried out in atemperature range in which noticeable back-reaction of the cyanuricfluoride formed already takes place. Thus, in sulfolanechlorodifluorotriazine is obtained at 140° C. in 5 h in 4% yield fromcyanuric fluoride in the presence of an 86% KCl/KF mixture. This is asalt mixture which is typically present after completion of thefluorination of cyanuric chloride with potassium fluoride using a 20%excess. At 190° C., more rapid conversion of cyanuric fluoride takesplace under otherwise identical conditions owing to fluorine/chlorineexchange. After about 10 h, 25% of the cyanuric fluoride is alreadyreacted to give chlorodifluoro- and dichlorofluorotriazine (cf. Examples1 and 2) On the other hand, this disadvantage--back-reaction of thecyanuric fluoride formed--does not occur if the reaction is carried outat temperatures up to about 110° C. (cf. Example 3). Cyanuric fluorideis thus formed rapidly and quantitatively. An equilibrium between mixedchlorinated/fluorinated triazines and cyanuric fluoride is notestablished.

In addition, a distinct saving of energy and thus a more economicsynthesis of cyanuric fluoride is possible compared to the previousprocesses for the preparation of cyanuric fluoride from cyanuricchloride or mixed chlorinated/fluorinated 1,3,5-triazines with alkalimetal fluorides at high temperatures.

The cyanuric fluoride is isolated in a manner customary per se by gentledistillation either in the presence of the alkali metal chloride orafter separating off the salt produced, a vacuum being used if desired.

In order to obtain cyanuric fluoride of high purity, complicatedseparation of mixed chlorinated/fluorinated 1,3,5-triazines is notnecessary since these are no longer contained in the reaction mixtureafter completion of the reaction.

The process according to the invention is illustrated in more detail bythe examples below, without being limited thereto. (In the examples,1,3,5-triazine is called "s-triazine".)

EXAMPLE 1 (COMPARISON EXAMPLE)

30.6 g of cyanuric fluoride are added at room temperature to asuspension of 70.3 g of KCl/KF mixture (86.5% by weight of KCl) in 138 gof dry sulfolane and the mixture is then stirred at 140° C. According togas chromatographic analysis ("GC analysis") of the reaction mixture, 4%of the cyanuric fluoride employed has been converted intochlorodifluorotriazine after 5 hours.

EXAMPLE 2 (COMPARISON EXAMPLE)

A reaction mixture as described in Example 1 is stirred at 190° C. After10 hours, according to GC spectrum [sic], the reaction mixture containss-triazines in the following distribution: 75% of cyanuric fluoride, 6%of chlorodifluoro-s-triazine and 19% of dichlorofluoro-s-triazine.

EXAMPLE 3

A reaction mixture as described in Example 1 is stirred at 100° C. for 5hours. According to GC, no fluorine/chlorine exchange can be detected inthe cyanuric fluoride. The cyanuric fluoride can be quantitativelyrecovered.

EXAMPLE 4

46.1 g of cyanuric chloride are added at 40° C. to a suspension of 52.3g of potassium fluoride in 175 g of dry sulfolane and the mixture isheated to 80° C. in the course of 20 minutes. After stirring for 80minutes at this temperature, the yield according to GC is 99.2% oftheory.

EXAMPLE 5

67.5 g of cyanuric chloride are mixed at 30° C. with a suspension of104.6 g of potassium fluoride in 300 g of sulfolane in a heat-insulatedreaction vessel. The reaction mixture heats uniformly to 97° C. within10 minutes. GC checking shows that cyanuric chloride has already reactedquantitatively to give cyanuric fluoride.

EXAMPLE 6

To a suspension of 384 g of potassium fluoride in 700 g of sulfolane at100° C., a solution of 369 g of cyanuric chloride in 500 g of sulfolane,also at 100° C., is added dropwise in the course of 2 hours. GC checkingof the reaction mixture shows that cyanuric chloride has reactedquantitatively to give cyanuric fluoride. Cyanuric fluoride is thendistilled off at a pressure of 500 to 100 mbar. The yield is 257 g (95%of theory); purity: 99.4 area % (GC).

EXAMPLES 7 TO 10

The procedure is analogous to Example 6. Amounts employed and yields aresummarized in the following table.

    ______________________________________                                                                   Cyanuric       Cyanuric                                   NaF    KF      CsF  chloride                                                                              Sulfolane                                                                            fluoride                            Example                                                                              [g]    [g]     [g]  [g]     [g]    [g]                                 ______________________________________                                        7      302    --      --   369     1000   251                                 8      134     13     --   184     550    122                                 9      --     191     19   184     700    126                                 10     139    --      14   184     550    125                                 ______________________________________                                    

EXAMPLE 11

30 g of a mixture of cyanuric chloride (8.6% by weight),dichlorofluoro-s-triazine (9.5% by weight), chlorodi-fluoro-s-triazine(16.4% by weight) and cyanuric fluoride (65.5% by weight) are added to20 g of KF in sulfolane and the mixture is stirred at 60° to 70° C.After 40 minutes, according to GC all chlorine-containing triazines havebeen converted into cyanuric fluoride.

EXAMPLE 12

A mixture of 184 g of cyanuric chloride, 209 g of potassium fluoride and900 g of sulfolane are heated to 100° C. for 4 hours in a 2 l autoclave.An overpressure of about 0.8 bar is established. According to GC,quantitative conversion of the cyanuric chloride to cyanuric fluoridetook place.

EXAMPLE 13

209 g of potassium fluoride are metered into 184 g of cyanuric chloridein 800 g of sulfolane at 100° C. in the course of 1 hour and the mixtureis then stirred at this temperature for a further hour. According to GC,the conversion of the cyanuric chloride to cyanuric fluoride isquantitative.

EXAMPLE 14

184 g of cyanuric chloride are reacted with 192 g of potassium fluorideanalogously to Example 6. After filtering off with suction the KCl/KFmixture obtained after completion of the reaction and washing it with600 g of chlorobenzene, cyanuric fluoride is distilled off from themother liquor. The yield is 129 g (96% of theory).

Purity: 99.9 area % (GC).

The boiling point of the cyanuric fluoride obtained and isolatedaccording to Examples 6 to 10 and 14 is 72.5 to 3.0° C.

EXAMPLE 15 (COMPARISON EXAMPLE)

A solution of 111 g of cyanuric chloride in 60 g of sulfolane at 140° C.is metered in the course of 15 minutes into a suspension of 90.8 g ofNaF in 104 g of sulfolane at 160° C. and the mixture is subsequentlystirred at 190° C. for 1 hour, altogether about 3/4 of the totalfluoride distilling over. The residual product is separated off at 500mbar to 50 mbar. The yield is 74.2 g (92% of theory). According to GC,the product has the following composition: cyanuric fluoride 97.7%,chlorodifluorotriazine 1.5%, dichlorofluorotriazine 0.5% and unknowncompounds 0.3%.

I claim:
 1. A process for the preparation of2,4,6-trifluoro-1,3,5-triazine (cyanuric fluoride) in high yield andhigh purity at relatively low temperatures, which comprises reacting2,4,6-trichloro-1,3,5-triazine (cyanuric chloride) or mixedchlorinated/fluorinated 1,3,5-triazines with at least the equivalentamount of sodium fluoride, potassium fluoride or cesium fluoride or anydesired mixture of these alkali metal fluorides in a dipolar aproticsolvent at temperatures from about 30° C. to about 110° C. and isolatingthe 2,4,6-trifluoro-1,3,5-triazine formed by distillation.
 2. Theprocess as claimed in claim 1, wherein the reaction is carried out attemperatures from about 50° C. to about 105° C.
 3. The process asclaimed in claim 1, wherein the reaction is carried out at temperaturesof about 70° C. to about 100° C.
 4. The process as carried out in claim1, wherein cyanuric chloride and/or mixed chlorinated/fluorinated1,3,5-triazines, the alkali metal fluoride or mixtures of the alkalimetal fluorides and the dipolar aprotic solvent are mixed and allowed toheat to the desired reaction temperature or are heated to the desiredreaction temperature.
 5. The process as claimed in claim 1, wherein thecyanuric chloride is metered into the suspension of the alkali metalfluoride or the mixture of the alkali metal fluorides in a dipolaraprotic solvent as a solid, as a melt or dissolved or suspended in aninert solvent.
 6. The process as claimed in claim 1, wherein the alkalimetal fluoride or the mixture of the alkali metal fluorides is meteredinto the mixture of cyanuric chloride and/or mixedchlorinated/fluorinated 1,3,5-triazines and the dipolar aprotic solventas a solid or as a suspension in an inert solvent.
 7. The process asclaimed in claim 1, wherein mixed chlorinated/fluorinated1,3,5-triazines or the cyanuric chloride, mixed with or dissolved inmixed chlorinated/fluorinated 1,3,5-triazines, is/are metered into thesuspension of the alkali metal fluoride or the mixture of the alkalimetal fluorides in a dipolar aprotic solvent, if desired with theaddition of an inert solvent.
 8. The process as claimed in claim 1,wherein the alkali metal chlorides produced are separated off before theisolation of the 2,4,6-trifluoro-1,3,5-triazine.
 9. The process asclaimed in claim 1, which process is carried out at normal pressure,reduced pressure or elevated pressure.